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OCR A-Level Physics A Edited > Chapter 23: Magnetic Fields > Flashcards

Chapter 23: Magnetic Fields Flashcards

1
Q

What is a magnetic field?

A

A region of space in which moving charged particles are subject to a magnetic force

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2
Q

What generates a circular magnetic field around a current-carrying wire?

A

The flowing electrons

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3
Q

What is a permanent magnet?

A

An object made from a magnetized material that creates its own persistent magnetic field

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4
Q

What demonstrates the magnetic field produced by a permanent magnet?

A

Iron filings

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5
Q

How do iron filings react in a magnetic field?

A

Their atoms align with the field, creating an induced magnetic field

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6
Q

What is the difference between magnetically hard and soft materials?

A

Soft materials can be magnetized but do not stay magnetized; hard materials do stay magnetized

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7
Q

What is the Earth’s magnetic field primarily due to?

A

The movement of charged particles within its molten iron core

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8
Q

True or False: The magnetic north of the Earth is actually in the northern hemisphere.

A

False

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9
Q

What do magnetic field lines represent?

A

The direction and strength of the magnetic field

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10
Q

What is the right-hand grip rule used for?

A

To determine the direction of the magnetic field around a current-carrying wire

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11
Q

What is Fleming’s Left-hand Rule used for?

A

To determine the direction of force on a current-carrying wire in a magnetic field

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12
Q

Fill in the blank: The force on a current-carrying wire in a magnetic field is greatest when the current is ______ to the magnetic field.

A

perpendicular

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13
Q

What is the unit of magnetic flux density?

A

Tesla (T)

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14
Q

What does the equation F = BIL sin θ represent?

A

The force on a current-carrying wire in a magnetic field

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15
Q

How can the magnetic flux density be determined experimentally?

A

Using the equation B = F/IL when the current is at right angles to the magnetic field

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16
Q

What happens to a charged particle moving in a uniform magnetic field?

A

It experiences a force perpendicular to its velocity

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17
Q

What is the result of the force acting on a free particle in a magnetic field?

A

The particle follows a curved trajectory

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18
Q

What does the term ‘centripetal acceleration’ refer to?

A

Acceleration towards the center of a circular path

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19
Q

What is the relationship between magnetic flux and magnetic flux density?

A

Magnetic flux density is the amount of magnetic flux per unit area

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20
Q

True or False: The speed of a charged particle changes when moving in a magnetic field.

A

False

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21
Q

What is the effect of a magnetic field on iron filings?

A

They align with the magnetic field

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22
Q

What is a solenoid?

A

A coil of wire that acts as an electromagnet when an electric current passes through it

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23
Q

Fill in the blank: The magnetic field lines for a solenoid are similar to that of a ______.

A

bar magnet

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24
Q

What does the density of magnetic field lines indicate?

A

The strength of the magnetic field

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25
What is the effect of increasing the number of turns in a coil on the magnetic field?
It causes a greater magnetic field
26
What is the purpose of using a soft core in an electromagnet?
To enhance the magnetic field produced by the coil
27
What occurs when a large magnetic field is applied in the reverse direction to a permanent magnet?
It demagnetizes the permanent magnet
28
What phenomenon causes the aurora borealis and aurora australis?
The interaction between the Earth's magnetic field and solar wind
29
What does the term 'magnetic flux' refer to?
The total magnetic field passing through a given area
30
What is the formula for the force on a single charge in a magnetic field?
F = BQv
31
How does the magnetic field of the Earth protect us?
It deflects harmful solar wind particles
32
What is the relationship between speed (v), radius (r), and force (F) in circular motion?
F = mv²/r ## Footnote This formula describes the centripetal force required for circular motion.
33
How does the radius of the circular motion depend on the properties of the particle?
r = m / B ## Footnote Here, m is the mass of the particle, and B is the magnetic field strength.
34
What is the significance of the momentum to charge ratio (p/Q) in particle motion?
Particles with a particular p/Q will undergo spiraling motion with a specific radius.
35
What apparatus is designed to visualize the tracks of ionizing particles?
Bubble chamber ## Footnote A bubble chamber makes the tracks of charged particles visible as bubbles in a liquid.
36
What is the function of a velocity selector?
Isolate particles with a specific velocity ## Footnote It uses a combination of electric and magnetic fields.
37
What is the formula for the electric force in a velocity selector?
F = EsQ ## Footnote Where Es is the electric field strength and Q is the charge.
38
What is the formula for the magnetic force in a velocity selector?
F = BsQv ## Footnote Where Bs is the magnetic field strength and Q is the charge.
39
In mass spectrometry, what happens to molecules before they are analyzed?
They are broken down into constituent atoms, ionized, and accelerated.
40
What is magnetic flux density (B)?
Magnetic flux per unit area.
41
How is magnetic flux (Φ) calculated for a uniform magnetic field?
Φ = BAcos θ ## Footnote Where θ is the angle between the magnetic field and the area.
42
What does electromagnetic induction refer to?
Induction of current due to a change in magnetic flux linkage.
43
What does Faraday's law of electromagnetic induction state?
ε ∝ Δ(N) / Δt ## Footnote Where ε is the induced e.m.f.
44
What is Lenz's law?
The induced e.m.f. opposes the change that produced it.
45
What happens to the induced current when a wire is stationary in a magnetic field?
The induced current falls to zero.
46
What is the purpose of a search coil?
Determine the strength of a magnetic field from induced current.
47
What is the primary function of a generator?
Convert kinetic energy into electrical energy.
48
What is the main principle behind the operation of an electric motor?
Produces a force on a coil when current passes through it.
49
What is the function of a split ring commutator in a DC motor?
Reverses the current direction to maintain a constant turning effect.
50
What is a transformer used for?
Raise or lower the voltage of alternating current sources.
51
What determines if a transformer is step-up or step-down?
The number of turns in the primary vs. secondary coil (Ns/Np).
52
How does a step-up transformer reduce power losses?
Increases voltage and decreases current for long-distance transmission.
53
What is the equation for the power loss in transmission lines?
Ploss = I²R ## Footnote Where R is the resistance of the transmission lines.
54
What is the role of transformers in mobile phone chargers?
Step down the voltage from mains supply to a safer level.
55
What is the purpose of a step-down transformer in a charger?
To lower the voltage supplied to the phone
56
Which device is preferred for measuring changing voltage in transformers?
Oscilloscope
57
What equation is used to estimate the efficiency of a transformer?
η = (Pₒ / Pᵢ) × 100%
58
What does the variable resistor (rheostat) do in transformer experiments?
Vary the current at a constant voltage
59
List three methods to make transformers more efficient.
* Using lower resistance wires in coils * Employing laminated iron in the core * Using soft iron cores
60
True or False: Eddy currents in the core of a transformer improve efficiency.
False
61
What is the effect of using laminated iron in a transformer core?
Channels magnetic flux more efficiently by reducing eddy currents
62
Fill in the blank: The efficiency of a transformer can be calculated as η = _______.
IₚVₚ / IₛVₛ × 100%
63
What type of wires can be used in transformer coils to reduce power loss?
Lower resistance wires
64
Why are soft iron cores preferred in transformers?
Easier to magnetize and demagnetize

OCR A-Level Physics A Edited (56 decks)

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